fix(dashboard): restore expert-mode manual model entry in the combo builder

PR #8285 (global model search) replaced the expert-mode "Manual model"
block positionally with the new GlobalModelSearchPanel, dropping the only
way to type a provider/model pair by hand in expert mode. The supporting
state and handlers (manualModelInput, manualModelError,
manualModelHasDuplicate, handleAddManualModel) survived as dead code, so
neither typecheck nor lint flagged the loss.

Re-render the block above the search panel, unchanged from its pre-#8285
form. Regression guard: tests/e2e/combos-flow.spec.ts "expert mode shows
a single-page combo form with manual model entry", which had been failing
with a 180s timeout on locator.fill for combo-manual-model-input.

src/app/(dashboard)/dashboard/combos/page.tsx

@@ -3227,6 +3227,51 @@ function ComboFormModal({ isOpen, combo, onClose, onSave, activeProviders, combo
                   )}
                 </div>
 
+                {isExpertMode && (
+                  <div className="mt-3 rounded-md border border-black/8 dark:border-white/8 bg-white/70 dark:bg-white/[0.03] px-2.5 py-2">
+                    <label className="text-[10px] font-medium uppercase tracking-wide text-text-muted block mb-1">
+                      {getI18nOrFallback(t, "manualModel", "Manual model")}
+                    </label>
+                    <div className="flex flex-col sm:flex-row gap-2">
+                      <input
+                        type="text"
+                        value={manualModelInput}
+                        onChange={(e) => {
+                          setManualModelInput(e.target.value);
+                          setManualModelError("");
+                        }}
+                        onKeyDown={(e) => {
+                          if (e.key === "Enter") {
+                            e.preventDefault();
+                            handleAddManualModel();
+                          }
+                        }}
+                        placeholder="provider/model"
+                        data-testid="combo-manual-model-input"
+                        className="flex-1 text-xs py-2 px-2 rounded border border-black/10 dark:border-white/10 bg-white dark:bg-white/5 text-text-main focus:border-primary focus:outline-none font-mono"
+                      />
+                      <Button
+                        onClick={handleAddManualModel}
+                        size="sm"
+                        disabled={!manualModelInput.trim() || !!manualModelHasDuplicate}
+                        data-testid="combo-manual-model-add"
+                      >
+                        {getI18nOrFallback(t, "addModel", "Add model")}
+                      </Button>
+                    </div>
+                    {(manualModelError || manualModelHasDuplicate) && (
+                      <div className="mt-2 rounded-md border border-amber-500/20 bg-amber-500/10 px-2 py-1.5 text-[10px] text-amber-700 dark:text-amber-300">
+                        {manualModelError ||
+                          getI18nOrFallback(
+                            t,
+                            "builderDuplicateExact",
+                            "This exact provider/model/account step is already in the combo."
+                          )}
+                      </div>
+                    )}
+                  </div>
+                )}
+
                 <GlobalModelSearchPanel
                   builderSelectionMode={builderSelectionMode}
                   onSelectionModeChange={setBuilderSelectionMode}